1. Field of the Invention
The present invention relates to a door interlock for electrical apparatus. More specifically, the present invention relates to an improved door interlock for electrical gear, which includes electrical apparatus within an enclosure, which interlock permits a door of the enclosure to be opened only if the electrical apparatus therewithin is in a certain condition and which prevents the condition of the apparatus from changing once the door is opened.
2. Brief Description of the Prior Art
Numerous door interlocks for electrical apparatus contained within an enclosure are known. See, for example, commonly assigned U.S. Pat. Nos. 4,073,000; 3,790,861; 3,748,621; and 3,339,118; and the following U.S. Pat. Nos. 4,118,607; 4,034,169, 3,991,291, 3,882,291; and 3,778,567. The typical environment of use for these prior art interlocks is within or as a part of the enclosure for the electrical apparatus which may include switches, movable between opened and closed positions. The interlocks may be associated with the switches in order to prevent the opening of a door for the enclosure as long as the switches are closed. With the switches closed and the electrical apparatus within the enclosure connected to an electrical circuit, electrical components within the enclosure are energized. With the switches opened, components, such as fuses, connected to the load side thereof are de-energized and may be handled or manipulated by workers. Prior art interlocks have, accordingly, often functioned to prevent the door from being opened until the switches within the enclosure are opened. Once these switches are opened and the door has been opened, the de-energized components in the enclosure may be handled or manipulated. Prior art interlocks also often prevent reclosing of the switches as long as the door is opened. This prevents the formerly de-energized components from becoming re-energized.
Many prior art interlocks, as functionally described above, suffer from one or more of three shortcomings. First, some interlocks are extremely complicated and, accordingly, are expensive and time-consuming to fabricate, manufacture and assemble. Second, the alignment, location or size of the parts of the interlocks must often be precisely controlled in order to ensure proper operation thereof. This is often quite difficult where the interlocks are complicated and contain numerous parts. Third, in many prior art interlocks, high forces are applied to non-robust parts which can cause both the failure thereof and the ultimate inability of the interlock to perform its intended functions.
A primary object of the present invention is the provision of an uncomplicated and inexpensive interlock which is convenient to fabricate, manufacture and assemble and which has a minimum of parts. A further object of the present invention is the provision of an interlock in which the need to precisely control the alignment, location and size of parts thereof is minimized, and the parts of which are not subjected to failure-producing high forces.